Electrical system

ABSTRACT

A method of monitoring an electrical system may include providing a ground fault detection unit, operating a transformer rectifier unit to provide DC power to a load, sensing, via a current sensor, a ground current at or about an output of the transformer rectifier, and/or monitoring a sensor output from the current sensor via the ground fault detection circuit. The ground fault detection circuit may be configured to detect ground faults at frequencies of at least 30 kHz.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of India Provisional PatentApplication Serial No. 201811021984, filed on Jun. 12, 2018, and IndiaProvisional Patent Application Serial No. 201811021985, filed on Jun.12, 2018, the disclosures of which are hereby incorporated herein byreference in their entireties.

TECHNICAL FIELD

The present disclosure generally relates to electrical systems,including ground fault detection systems that may be configured forwideband ground fault detection for high voltage direct current (DC),high voltage alternating current (AC), and/or high frequency switchingcurrents.

BACKGROUND

This background description is set forth below for the purpose ofproviding context only. Therefore, any aspect of this backgrounddescription, to the extent that it does not otherwise qualify as priorart, is neither expressly nor impliedly admitted as prior art againstthe instant disclosure.

Electrical systems may continue to use higher voltages and/or highercurrents, which may involve changes to existing systems. For example andwithout limitation, the increase in onboard electrical power generation(e.g., of aircraft) has resulted in significant changes to electricalpower system architectures to ensure efficiency benefits of electricalloads are not mitigated. Higher voltage levels may enable moredistributed architectures. Variable frequency AC and DC sections may beused, or more extensively used, in aircraft electrical networks/systemsthat may be critical to the operation of the aircraft. PWM (pulse widthmodulation) converters and battery-based architectures may involve DC/DCconverters, DC/AC motor drives, AC/DC chargers or power converters,and/or other components operating with high frequencies (e.g., PWM,switching, etc.), such as for achieving higher power density, lowerweight, and increased efficiency. Such high frequency components maycause noise and/or result capacitive coupling, such as due tofundamental and harmonic frequencies.

High voltages and/or high frequencies may be utilized, and the risk of aground fault may be increased relative to systems utilizing lowervoltages and/or lower frequencies. It may be desirable for an electricalsystem, such as an aircraft electrical system, to include an electricalprotection/detection system. An electrical protection/detection systemmay detect and appropriately respond to faults, such that (in theworst-case scenario) an aircraft is able to land safely after anelectrical fault has occurred.

Existing ground fault detection (GFD) devices, such as those that may beused in connection with aircraft, may only be intended for 115 VAC, 360Hz to 800 Hz. Newer aircraft electrical systems may be “More ElectricAircraft” (MEA) systems and/or fully electric systems, which may involveelectrical systems utilizing higher nominal voltages, and/or frequenciessuch as, for example and without limitation, 230 VAC, +/−270 VDC, and/or+/−540 VDC, with frequencies that may be on the order of severalkilohertz to tens of megahertz, or higher. The chances of a ground faultoccurrence with high voltage and high current systems may be moreprominent than with lower voltage and current systems that may be usedin conventional electrical/aircraft systems. Carbon composite aircrafts(CFRP) may be vulnerable to arcing and ground faults. Also, highfrequency motor drives may introduce high frequency ground faults and DCground faults that may not be an issue for existing designs. Also, a DCground fault can saturate some conventional current measurement systems.

There is a desire for solutions/options that minimize or eliminate oneor more challenges or shortcomings of electrical systems. The foregoingdiscussion is intended only to illustrate examples of the present fieldand should not be taken as a disavowal of scope.

SUMMARY

In embodiments, a method of monitoring an electrical system may includeproviding a ground fault detection unit, operating a transformerrectifier unit to provide DC power to a load, sensing, via a currentsensor, a ground current at or about an output of the transformerrectifier, and/or monitoring a sensor output from the current sensor viathe ground fault detection circuit. The ground fault detection circuitmay be configured to detect ground faults at frequencies of at least 30kHz. The ground fault detection unit may be configured to detect groundfaults at frequencies of at least 100 kHz. The method may includesensing, via a second current sensor, the ground current. The currentsensor may be configured as a high-frequency current sensor and thesecond current sensor is a low-frequency current sensor. The currentsensor may not be a Hall Effect sensor. The second current sensor may bea Hall Effect sensor. Monitoring the sensor output may includemonitoring the sensor output over a period of time. The period of timemay be at least one hour. The method may include detecting a groundfault if the ground current exceeds a first threshold or a secondthreshold. The first threshold may be a low frequency current thresholdand the second threshold may be a high frequency current threshold. Thesecond threshold may be lower than the first threshold. Detecting theground fault may include detecting the ground fault if the groundcurrent exceeds the first threshold for a first period of time or if theground current exceeds the second threshold for a second period of time.The second period of time may be longer than the first period of time.The ground fault may correspond to ground current with a frequency of atleast 25 kHz. Detecting the ground fault may include detecting theground fault without a Fourier transform.

With embodiments, an electrical system may include a ground faultdetection unit, including a first ground fault detection circuit and/ora second ground fault detection circuit. The first ground faultdetection circuit may include a first portion and a second portion. Thefirst portion and the second portion may be connected to a first currentsensor. The second ground fault detection circuit may include a firstportion and a second portion. The first portion and the second portionmay be connected to a second current sensor. The first current sensorand the second current sensor may be configured to sense current at orabout an output of a DC power supply. The first portion of the firstground fault detection circuit may include a low pass filter having acutoff frequency. The second portion of the first ground fault detectioncircuit may include a first bandpass filter with a first passband. Thefirst portion of the second ground fault detection circuit may include asecond bandpass filter with a second passband; and the second portion ofthe second ground fault detection circuit may include a third bandpassfilter with a third passband. The third passband may include higherfrequencies than the second passband. The second passband may includehigher frequencies than the first passband. The first passband mayinclude frequencies above the cutoff frequency.

In embodiments, the DC power supply may include a transformer rectifierunit. The first passband may correspond to the DC power supply. Thesecond passband may correspond to switching frequencies. The thirdpassband may correspond to harmonics of the switching frequencies. Amaximum frequency of the third passband may be at least about 100 kHzand a maximum frequency of the second passband may be at least about 20kHz. A maximum frequency of the second passband may be at least about 4kHz. The cutoff frequency may be about 10 Hz or less. The first portionof the second ground fault detection circuit may include a demodulatorconfigured to reduce a frequency of an output of the second currentsensor. The first portion of the first ground fault detection circuitmay include a monostable multivibrator.

With embodiments, an electrical system may include a second ground faultdetection unit including a third ground fault detection circuit and afourth ground fault detection circuit. The second ground fault detectionunit may be connected to an AC power supply. The DC power supply may beconnected to the AC power supply and may be configured to convert ACpower from the AC power supply to DC power for a variable frequencydrive connected to an electric motor.

The foregoing and other aspects, features, details, utilities, and/oradvantages of embodiments of the present disclosure will be apparentfrom reading the following description, and from reviewing theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view generally illustrating an embodiment of anelectrical system according to teachings of the present disclosure.

FIG. 2 is a schematic view generally illustrating portions of anembodiment of an electrical system according to teachings of the presentdisclosure.

FIG. 3 is a schematic view generally illustrating an embodiment of aground fault detector according to teachings of the present disclosure.

FIG. 4 is a schematic view generally illustrating portions of anembodiment of an electrical system, with a ground fault detector,according to teachings of the present disclosure.

FIG. 5 is a graphical view of ground current in an embodiment of anelectrical system according to teachings of the present disclosure.

FIG. 6 is a graphical view of the frequencies of ground current in anembodiment of an electrical system according to teachings of the presentdisclosure.

FIG. 7 is a schematic view generally illustrating portions of anembodiment of an electrical system according to teachings of the presentdisclosure.

FIG. 8 is a schematic view generally illustrating portions of anembodiment of an electrical system, including a low frequency groundfault detection circuit and a high frequency detection circuit,according to teachings of the present disclosure.

FIG. 9 is a schematic view generally illustrating portions of anembodiment of an electrical system including a low frequency groundfault detection circuit according to teachings of the presentdisclosure.

FIG. 10 is a schematic view generally illustrating portions of anembodiment of an electrical system including a high frequency groundfault detection circuit according to teachings of the presentdisclosure.

FIG. 11 is a schematic view generally illustrating an embodiment of atransformer rectifier unit according to teachings of the presentdisclosure.

FIG. 12 is a schematic view generally illustrating an embodiment of atransformer rectifier unit according to teachings of the presentdisclosure.

FIG. 13 is a schematic representation generally illustrating groundfaults associated with an embodiment of a transformer rectifier unit(TRU) according to teachings of the present disclosure.

FIG. 14 is a graphical view of input and output voltages of anembodiment of a transformer rectifier unit of an electrical systemaccording to teachings of the present disclosure.

FIG. 15 is a graphical view of input voltage and input current of anembodiment of a transformer rectifier unit of an electrical systemaccording to teachings of the present disclosure.

FIG. 16 is a graphical view of a harmonic spectrum of input current ofan embodiment of a transformer rectifier unit of an electrical systemaccording to teachings of the present disclosure.

FIG. 17 is a graphical view of frequencies of ground current in anembodiment of an electrical system according to teachings of the presentdisclosure.

FIG. 18 is a schematic view generally illustrating portions of anembodiment of an electrical system, including a low frequency groundfault detection circuit and a high frequency detection circuit,according to teachings of the present disclosure.

FIG. 19 is a schematic view generally illustrating portions of anembodiment of an electrical system including a low frequency groundfault detection circuit according to teachings of the presentdisclosure.

FIG. 20 is a schematic view generally illustrating portions of anembodiment of an electrical system including a high frequency groundfault detection circuit according to teachings of the presentdisclosure.

FIG. 21 is a schematic view generally illustrating portions of anembodiment of a current sensor according to teachings of the presentdisclosure.

FIG. 22 is a graphical view of the impedance and frequency of variouscurrent sensors, including an embodiment of a current sensor accordingto teachings of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentdisclosure, examples of which are described herein and illustrated inthe accompanying drawings. While the present disclosure will bedescribed in conjunction with embodiments and/or examples, it will beunderstood that they are not intended to limit the present disclosure tothese embodiments and/or examples. On the contrary, the presentdisclosure is intended to cover alternatives, modifications, andequivalents.

In embodiments, such as generally illustrated in FIG. 1, an electricalsystem 100 may include a power source 102, an electronic control unit(ECU) 104, a plurality of loads 106, a first ground fault detection(GFD) unit 110, a second GFD unit 120, and one or more additional GFDunits (e.g., GFD units 122, 124, 126, 128). Additional GFD units 122,124, 126, 128 may be configured in the same or a similar manner as GFDunits 110, 120, as appropriate. Two or more of the GFD units 110, 120,122, 124, 126, 128 may be configured to communicate with each other. Thepower source 102 may be connected directly to one or more loads (e.g.,first loads 130) and/or the power source 102 may be connected indirectlyconnected to one or more loads, (e.g., second loads 132, third loads134, fourth loads 136, and/or fifth loads 138), such as via transformersand/or power distribution units. For example and without limitation, thepower source 102 may be connected to one or more second loads 132 via anauto-transformer unit (ATU) 140 and/or a first power distribution unit(PDU) 142; the power source 102 may be connected to one or more thirdloads 134 via a transformer rectifier unit (TRU) 144 and/or a second PDU146; the power source 102 may be connected to one or more fourth loads136 via an auto-transformer rectifier unit (ATRU) 148; the power source102 may be connected to one or more remote loads 150 via one or moreremote power distribution units (RPDUs) 152, which may be connected tothe power source 102 via the power distribution units 142, 146, the ATU140, and/or the TRU 144; and/or the power source 102 may be connected toone or more fifth loads 138 via one or more converters 154, which mayinclude DC/DC converters, AC/AC converters, AC/DC converters, and/orDC/AC converters. One or more of the converters 154 may have a variablefrequency and/or may introduce variable and/or high frequency componentsinto the electrical system 100.

With embodiments, the power source 102 may be configured to provide ACpower and/or DC power. The power source 102 may, for example and withoutlimitation, include generators that may be connected to engines (e.g.,aircraft engines) and/or an auxiliary power unit (APU), may include onemore batteries, and/or may include other power sources.

In embodiments, the first loads 130 may include one or more of a varietyof loads, such as, for example and without limitation, a wing iceprotection system (WIPS), a hydraulic AC motor pump, fuel pumps, galleyovens, cargo heaters, and/or environmental control system (ECS)recirculation fans, among others. The first loads 130 may, for example,be configured to operate with about 230 VAC.

With embodiments, the second loads 132 may include one or more of avariety of loads, such as, for example and without limitation, ECSlavatory/galley fans, equipment cooling fans, and/or window heaters,among others. The second loads 132 may, for example, be configured tooperate with about 115 VDC. An ATU 140 may be configured to convertpower from the power source 102 (e.g., 230 VAC) to the operating voltageof the second loads 132 (e.g., 115 VDC) and/or the first PDU 142 may beconfigured to provide 115 VDC to the second loads 132.

In embodiments, the third loads 134 may include one or more of a varietyof loads, such as, for example and without limitation, a DC fuel pump,igniters, a common core system (CCS), flight deck displays, a bus powercontrol unit (BPCU), and/or a generator control unit (GCU), amongothers. The third loads 134 may be configured to operate with 28 VDC.The TRU 144 may be configured to convert power from the power source 102(e.g., 230 VDC) to an operating voltage of the third loads 134, such as28 VDC, and/or the second PDU 146 may be configured to provide theoperating voltage to the third loads 134.

With embodiments, the fourth loads 136 may include one or more of avariety of loads, such as, for example and without limitation,adjustable speed motors that may be controlled via one or morecontrollers that may be connected to the ATRU. A controller may includea variable frequency generator/drive (VFD) for controlling an adjustablespeed electric motor. The ATRU 148 may be configured to convert powerfrom the power source 102 (e.g., 230 VAC) to an operating voltage of thefourth loads 136, such as 270 VDC.

In embodiments, such as generally illustrated in FIG. 2, a fourth load136 (e.g., a motor) may include a stator 160, a rotor 162, a shaft 164,and/or a housing 166. A controller 168 may provide a control signal tothe stator 160 to cause rotation of the rotor 162 and the shaft 164 toactuate a mechanical load 170. The frequency range of the controller 168may, for example and without limitation, include a lower end of about 10kHz and may include an upper end of about 50 kHz. As the shaft 164rotates, some electrical current (e.g., high frequency current) may betransferred from the shaft 164 to the housing 166, such as via a bearing172 (e.g., via capacitive and/or inductive coupling), and the housing166 may be connected to ground, which may result in ground current. Thisground current may be harmful to the electrical system 100. For exampleand without limitation, the ground current may cause physical damage, atleast over time, to the bearing 172, which may result in bearingfailure.

Examples of ground fault detectors (GFDs) 180, 182 are generallyillustrated in FIGS. 3 and 4. A GFD 180, 182 may be configured to detectground current. For example and without limitation, a GFD 182 may beconnected between a power supply 184 and a motor 186 and/or acontroller/variable frequency drive (VFD) 188 (or PMSM or BLDC drives)associated with the motor 186. The VFD 188 may include an EMI(electromagnetic interference) filter 190, a rectifier 192, a DC link194, and/or an IGBT (insulated-gate bipolar transistor) drive 196. Theexample systems 180, 182 may be based upon a summation of a common modetransformer. If the sum of I1, I2, and I3 is non-zero (e.g., Ig isnon-zero), then depending upon a threshold of allowable ground current,the system may detect the ground fault (see, e.g., FIG. 3). As generallyillustrated in FIG. 4, sources of ground current may include the EMIfilter 190 and/or a DC link 194 of the VFD 188, and/or the motor 186,for example and without limitation. As generally illustrated in FIG. 5,if a motor 186 accelerates, the ground current associated with the motor186 and/or the system may increase.

With embodiments, such as generally illustrated in FIG. 6, groundcurrent may include a plurality of frequencies. Some current sensors maybe configured to sense current at relatively low frequencies, such asabout 400 Hz or less, but such sensors may not effectively sense groundcurrent at higher frequencies, such as, for example, frequencies ofabout 20 KHz to about 400 KHz or higher. In some circumstances, thenoise content (e.g., spectral noise) of AC GF currents above 2 A in theregion of 100 kHz may be of the order of 50 dBμA (300 μA) and at 2 MHzmay be of the order of 20 dBμA (10 μA). Conventional sensors may notoffer this wide dynamic range. Noise content may be measured in animpedance-controlled test setup using a spectrum analyzer and an RFcurrent probe.

FIG. 7 generally illustrates portions of an embodiment of an electricalsystem 100, which may be configured as an MEA power distribution system.An electrical system 100 may include a power source 102 that may includea first generator 200, a first generator controller 202, a secondgenerator 204, and/or a second generator controller 206. The powersource 102 may be configured to provide power to one or more loads, suchas a first electronic climate system (ECS) 208, a second ECS 210, afirst electromechanical actuator (EMA) 212, a second EMA 214, a wing iceprotection system (WIPS) 216, and/or one or more other loads 218. Thefirst ECS 208, the second ECS 210, the first EMA 212, and/or the secondEMA 214 may include a motor 2201, 2202, 2203, 2204, such as a permanentmagnet motor (PMM). A first ATRU 222 may be connected between the powersource 102 and the first ECS 208. A second ATRU 224 may be connectedbetween the power source 102 and the second ECS 210. The first EMA 212may include a first controlled rectifier unit (CRU) 226 and/or a firstcontrolled inverter unit (CIU) 228. The second EMA 214 may include asecond CRU 230 and/or a second CIU 232. A breaker, generally designatedwith S, may be disposed at some or all junctions. A circuit breaker S atthe power source 102 or at the load side may be capable of dealing with(e.g., detecting) at least some ground faults, such as lower frequencyground faults.

With embodiments, an ATRU 222, 224 may create a frequency component thatmay be different than the power source 102. For example and withoutlimitation, the frequency component associated with an ATRU may be about12 times the frequency of the power source 102. Isolation may not beavailable for an ATRU 222, 224. Additionally or alternatively, CRUs 226,230 may create switching frequency noise. Embodiments of electricalsystems 100 may incorporate and/or be configured to implement designtechniques and solutions to limit damage from ground faults.

In embodiments, a plurality of primary energy bands (e.g., four primaryenergy bands) may be identified as likely to indicate/reflect a groundfault. The bands may be identified by statistical analysis. A first bandmay, for example and without limitation, include about 0 Hz to about 1KHz, such as about 0 Hz to about 10 Hz (e.g., for DC current) and/orabout 300 Hz to about 900 Hz (e.g., for AC current). The first band mayinclude significant low frequency (LF) GF energy and/or may include theaircraft supply frequency band, which may be about 400 Hz. A secondfrequency band may, for example and without limitation, include about 4kHz to about 10 kHz. The TRU/ATRU and AC leakages on a secondarytransformer may be present in the second band. A third frequency bandmay, for example and without limitation, include about 20 kHz to about50 kHz. Ground currents due to switching frequency may be present in thethird band. A fourth band may, for example and without limitation,include about 150 kHz to 400 kHz. The fourth band may include harmonicsof switching frequencies. It may be possible to tune these bands toanother set of frequencies. If information about the switchingcharacteristics of the load side equipment is available, suchinformation can be entered (e.g., into an ECU 104) using userprogrammable inputs, which may facilitate tuning of these bands (e.g.,for ground fault detection units 110, 120) and avoid/limit nuisancetripping. Sensing directly at these harmonics may facilitate detectingground faults. If such information is not available, then defaultsettings can be used. In embodiments, an ECU 104, a first GFD unit 110,and/or a second GFD unit 120 of an electrical system 100 mayextract/evaluate some or all of these wideband GF characteristics andmay make a decision to trip (e.g., open a circuit, disconnect acomponent, etc.).

Utilizing a single current sensor (CS) to cover low frequency (LF) andhigh frequency (HF) fault current components may not be practical insome circumstances. In embodiments, an electrical system 100 may includetwo current probes/sensors, such as an LF current sensor 236 and an HFcurrent sensor 238. An electrical system 100 may include one or more LFcurrent sensors 236, which may include Hall Effect sensors. Anelectrical system 100 may include one or more HF current sensors 238,which may include toroidal transformers. Additionally or alternatively,an HF current sensor 238 may include a single current shunt or wide bandcurrent transformer that may be followed by different active or passiveband selective filters (e.g., in a GFD unit 110, 120). For low frequencycurrent, an LF current sensor 236 may include a common mode choke/hallprobe may be utilized to detect 0 Hz to 1 kHz output signals (e.g., 0 Hzto 10 Hz, 300 Hz to 900 Hz, etc.) which may be further analyzed by a GFDunit 110, 120 and/or an electronic control unit 104, such as todetermine the presence of a ground fault. The GFD unit 110, 120 and/orthe ECU 104 may utilize a built-in method that may compare parameters ofincoming signals against threshold values. These thresholds may, forexample and without limitation, be programmed in real-time using digitalpotentiometers and/or may be preset.

An embodiment of an electrical system 100 that may be configured forground fault detection is generally illustrated in FIG. 8. Theelectrical system 100 may include a first GFD unit 110, a DC powersupply 240, an ECU 104, output drivers 242, and/or one or more outputs,such as a contactor interface 244 and/or one or more LEDs (lightemitting diodes) 246, for example and without limitation. The DC powersupply 240 may provide power to the first GFD unit 110 and/or the ECU104. The ECU 104 may be connected to and/or configured to control thefirst GFD unit 110 and/or the output drivers 242. The output drivers 242may drive the outputs 244, 246. The first GFD unit 110 may include amicrocontroller unit (GFCU) 110A, an LF GFD circuit 250 and/or an HF GFDcircuit 350. An embodiment of an LF GFD circuit 250 is generallyillustrated in FIG. 9. An embodiment of an HF GFD circuit 350 isgenerally illustrated in FIG. 10.

With embodiments, such as generally illustrated in FIG. 9, an LF GFDcircuit 250 may include a first portion 260 and/or a second portion 280,which may be connected to the GFCU 110A. The first portion 260 may beconfigured to detect ground faults in a first range of frequencies, suchas about 300 Hz to about 900 Hz. The second portion 280 may beconfigured to detect ground faults in a second range of frequencies,such as about 4 KHz to about 10 KHz.

In embodiments, the first portion 260 may include signal conditioningcircuitry 262, a filter 264, a rectifier and peak detector 266 (e.g., aprecision rectifier and peak detector), a zero-crossing detector 268,and/or a threshold-crossing detector 270. An LF current sensor 236 maybe connected at or about an output of the power source 102 (e.g.,connected to sense the current(s) of the output signal(s) of the powersource 102). An output of the LF current sensor 236 may be connected tothe signal conditioning circuitry 262. An output of the signalconditioning circuitry 262 may be connected to the filter 264. Thefilter 264 may be configured as a bandpass filter that may include afirst passband. The first passband may, for example and withoutlimitation, include about 300 Hz to about 900 Hz. An output of thefilter 264 may be connected to the rectifier and peak detector 266. Anoutput of the rectifier and peak detector 266 may be connected to theGFCU 110A, the zero-crossing detector 268, and/or the threshold-crossingdetector 270. An output of the zero-crossing detector 268 and/or anoutput of the threshold-crossing detector 270 may be connected to theGFCU 110A. The threshold-crossing detector 270 may compare the output ofthe rectifier and peak detector 266 to a threshold and the output of thecomparison may be transferred to an input port of the GFCU 110A. Asignal transition on this input port may indicate that current hascrossed the ground threshold and further action may be initiated by theGFCU 110A (e.g., disconnection, shut down, etc.). The peak of therectified signal may be held substantially constant for a specificduration and may be read by the GFCU 110A. The GFCU 110A may thendischarge the peak detector 266. The GFCU 110A may process thisinformation and may determine if the content of the first portion 260 ofLF GFD circuit 250 indicates the presence of a ground fault. For exampleand without limitation, the GFCU 110A may use results of comparisons toincrease or decrease the number of events recorded by a counter, and thepresence of a fault may be established when the number of counts reachesthe predetermined threshold value, such as within a selected slidingtime window.

In embodiments, the GFCU 110A may be configured to receive an input(e.g., user input) to set a threshold of the threshold-crossing detector270. The GFCU 110A may set the threshold according to the input.Additionally or alternatively, a default threshold may be provided, suchas via a potentiometer 272.

With embodiments, the second portion 280 of the LF GFD circuit 250 mayinclude signal conditioning circuitry 282, a filter 284, an invertingamplifier 286, a demodulator 288 (e.g., a radio frequency or RFdemodulator), a threshold comparator 290, and/or a timer circuit 292. Anoutput of the LF current sensor 236 may be connected to the signalconditioning circuitry 282. An output of the signal conditioningcircuitry 282 may be connected to the filter 284. The filter 284 may beconfigured as a bandpass filter that may include a second passband. Thesecond passband may, for example and without limitation, include about 4KHz to about 10 KHz. An output of the filter 284 may be connected to theinverting amplifier 286. An output of the inverting amplifier 286 may beconnected to the demodulator 288. An output of the demodulator 288 maybe connected to the GFCU 110A and/or to the threshold comparator 290. Anoutput of the threshold comparator 290 may be connected to a timercircuit 292. An output of the timer circuit 292 may be connected to aninput of the GFCU 110A. The GFCU 110A may process information from thedemodulator 288 and/or the timer circuit 292 and may determine if thecontent of the second portion 280 indicates the presence of a groundfault.

In embodiments, the GFCU 110A may be configured to receive an input(e.g., user input) to set a threshold of the threshold comparator 290.The GFCU 110A may set the threshold according to the input. Additionallyor alternatively, a default threshold may be provided, such as via apotentiometer 294.

With embodiments, the second portion 280 may be connected to an HFcurrent sensor 238 in addition to and/or instead of the LF currentsensor 236 that may be connected to the first portion 260 (e.g., thesecond portion 280 may be part of the HF GFD circuit 350).

In embodiments, such as generally illustrated in FIG. 10, an HF GFDcircuit 350 may include a first portion 380 and/or a second portion 480.The first portion 380 may be configured to detect ground faults in athird range of frequencies, such as about 20 KHz to about 50 Hz. Thesecond portion 480 may be configured to detect ground faults in a fourthrange of frequencies, such as about 150 KHz to about 350 KHz. Withembodiments, the first portion 380 and the second portion 480 of the HFGFD circuit 350 may be configured in a similar manner as the secondportion 280 of the LF GFD circuit 250, except for the configuration ofthe filters. For example and without limitation, the first portion 380and the second portion 480 may each include signal conditioningcircuitry 382, 482, a filter 384, 484, an inverting amplifier 386, 486,a demodulator 388, 488 (e.g., a radio frequency or RF demodulator), athreshold comparator 390, 490, and/or a timer circuit 392, 492. Thefilter 384 of the first portion 380 may include a third passband thatmay, for example, include about 20 KHz to about 50 Hz. The filter 484 ofthe second portion 480 may include a fourth passband that may, forexample, include about 150 KHz to about 350 KHz. The GFCU 110A may beconfigured to receive an input (e.g., user input) to set thresholds ofthe threshold comparators 390, 490. The GFCU 110A may set the thresholdsaccording to the input. Additionally or alternatively, defaultthresholds may be provided, such as via potentiometers 394, 494.

With embodiments, the demodulators 288, 388, 488 may be configured toreduce the frequency of the incoming signal (e.g., from the HF currentsensor 238), which may facilitate comparing the incoming signal to thethreshold and/or the GFCU 110A analyzing the output of the first GFDunit 110. Such a configuration may allow an electrical system 100 todetect a high frequency ground fault without using digital signalprocessing and Fourier transforms that may involve complex calculationsand/or powerful processors. For example and without limitation, thefirst GFD unit 110 may be configured to process the output of a currentsensor 238 via hardware/circuitry (e.g., analog processing) instead ofthe GFCU 110A or the ECU 104 performing complex calculations.

With embodiments, one or more of the filters 264, 284, 384, 484 may, forexample and without limitation, be configured as a Sallen-Key bandpassfilter.

In embodiments, such as generally illustrated in FIGS. 1 and 7, an ACvoltage may be generated via the power source 102 (e.g., a variable ACsupply) and the AC voltage may be converted to a DC voltage via anauto-transformer rectifier unit (ATRU) 148, 222, 224. The ATRU 148, 222,224 may enable significant weight reduction relative to other AC/DCconversion configurations. FIGS. 11 and 12 generally illustrate examplearchitectures and internal blocks of an ATRU 148, 222, 224. As generallyillustrated in FIG. 12, an ATRU 148, 222, 224 may include anauto-transformer 500 (e.g., a 12-pulse auto-transformer), a rectifier502, interphase reactors 504, a differential mode choke 506, a bulkcapacitor 508, and/or load capacitors 510, and may be connected to aload 512. An electrical system 100 may be configured for wide and/ordynamic range measurement, such as for DC and/or high frequency faultsthat may result, at least in part, from an ATRU 148, 222, 224.

In embodiments, an output of a TRU/ATRU and a filter for 3 phase 115 VAC supply may be about +/270 V DC (see, e.g., FIGS. 14 and 15). A groundfault in a TRU-based DC system can occur because of positive to groundand/or negative to ground conduction (see, e.g., FIG. 13).Typical/conventional GFD systems may rely on a 150-200% overcurrenttrip, which may be due to low impedance of the ground. Theseconventional systems may be insensitive to high frequency currents (see,e.g., FIG. 17), which can be of low amplitude but can cause structuraldamage, such as to bearings of a motor, at least over periods of time.Conventional current sensors may not provide a wide dynamic range.

In some circumstances, such as generally illustrated in FIG. 16, thenext peak after fundamental may be at or about 11 times the supplyfrequency. A leakage/ground current due to an ATRU 148, 222, 224 mayalso be at or about 11 times the input frequency, for example.

In embodiments, DC loads may be connected to a TRU/ATRU and may involveswitching converters. With embodiments, an electrical system 100 mayincorporate and/or be configured to implement design techniques andsolutions to limit damage from ground faults. A GFD unit 110, 120at/near the power source 102 and/or at the load side of the electricalsystem 100 may include a separate floating return and may be madecapable of detecting wideband DC ground faults. DC ground faults mayhave fixed low frequency DC and/or high frequency switching current.

An embodiment of an electrical system 100 (e.g., a GFD system) isgenerally illustrated in FIG. 18 and may include a second GFD unit 120,a DC power supply 540, a GFCU 120A, output drivers 542, and/or one ormore outputs, such as a contactor interface 544 and/or one or more LEDs(light emitting diodes) 546, for example and without limitation. The DCpower supply 540 may provide power to the second GFD unit 120. The GFCU120A may be connected to and/or configured to control the second GFDunit 120 and/or the output drivers 542. The output drivers 542 may drivethe outputs 244, 546. The second GFD unit 120 may include an LF GFDcircuit 550 and/or an HF GFD circuit 650. An embodiment of an LF GFDcircuit 550 is generally illustrated in FIG. 19. An embodiment of an HFGFD circuit 650 is generally illustrated in FIG. 20.

With embodiments, such as generally illustrated in FIG. 19, an LF GFDcircuit 550 may include a first portion 560 and/or a second portion 580.The first portion 560 may be configured to detect ground faults in afirst range of frequencies, such as about 0 Hz to about 10 Hz. The firstportion 560 may include a configuration that may be similar to the firstportion 260 of the LF GFD circuit 250 of the first GFD unit 110described in connection with FIG. 9. For example and without limitation,the first portion 560 of the LF GFD circuit 550 may include signalconditioning circuitry 562, a filter 564, a rectifier and peak detector566 (e.g., a precision rectifier and peak detector), and/or azero-crossing detector 568. The first portion 560 may include amonostable multivibrator 570. The filter 564 may be configured as a lowpass filter that may include a cutoff frequency of about 10 Hz or less(or more). An LF current sensor 572 may be connected at or about anoutput of a TRU/ATRU (e.g., ATRU 148, 222, or 224) and may be connectedto the signal conditioning circuitry 562.

With embodiments, the second portion 580 may be configured to detectground faults in a second range of frequencies, such as about 4 KHz toabout 10 KHz. The second portion 580 may be configured in the same or asimilar manner as the second portion 280 of the LF GFD circuit 250 ofthe first GFD unit 110 described in connection with FIG. 9. For exampleand without limitation, the second portion 580 of the LF GFD circuit 550may include signal conditioning circuitry 582, a filter 584, aninverting amplifier 586, a demodulator 588 (e.g., a radio frequency orRF demodulator), a threshold comparator 590, and/or a timer circuit 592.An output of the LF current sensor 572 may be connected to the signalconditioning circuitry 582. The filter 584 may be configured as abandpass filter that may include a first passband. The first passbandmay, for example and without limitation, include about 4 KHz to about 10KHz. With embodiments, the second portion 580 may be connected to an HFcurrent sensor 600 in addition to and/or instead of the LF currentsensor 572 that may be connected to the first portion 560. The GFCU 120Amay be configured to receive input (e.g., user input) to set thresholdsof the threshold comparator 590. The GFCU 120A may set the thresholdsaccording to the input. Additionally or alternatively, defaultthresholds may be provided, such as via a potentiometer 594.

In embodiments, such as generally illustrated in FIG. 20, an HF GFDcircuit 650 may include a first portion 680 and/or a second portion 780.The first portion 680 may be configured to detect ground faults in athird range of frequencies, such as about 20 KHz to about 50 Hz. Thesecond portion 780 may be configured to detect ground faults in a fourthrange of frequencies, such as about 150 KHz to about 400 KHz. Withembodiments, the first portion 680 and the second portion 780 of the HFGFD circuit 650 may be configured in the same or a similar manner as thefirst portion 380 and the second portion 480, respectively, of the HFGFD circuit 350 of the first GFD unit 110 described in connection withFIG. 10. For example and without limitation, the first portion 680 andthe second portion 780 may each include signal conditioning circuitry682, 782, a filter 684, 784, an inverting amplifier 686, 786, ademodulator 688, 788 (e.g., a radio frequency or RF demodulator), athreshold comparator 690, 790, and/or a timer circuit 692, 792. Thefilter 684 of the first portion 680 may include a second passband thatmay, for example, include about 20 KHz to about 50 Hz. The filter 784 ofthe second portion 780 may include a third passband that may, forexample, include about 150 KHz to about 350 KHz. The GFCU 120A may beconfigured to receive input (e.g., user input) to set thresholds of thethreshold comparators 690, 790. The GFCU 120A may set the thresholdsaccording to the input. Additionally or alternatively, defaultthresholds may be provided, such as via potentiometers 694, 794.

With embodiments, the demodulators 588, 688, 788 may be configured toreduce the frequency of the incoming signal (e.g., from the HF currentsensor 600), which may facilitate comparing the incoming signal to thethreshold. Such a configuration may allow an electrical system 100 todetect a high frequency ground fault without using of digital signalprocessing and Fourier transforms that may involve complex calculationsand/or powerful processors.

In embodiments, such as generally illustrated in FIGS. 10 and 20, anoutput of an HF current sensor 238, 600 may be conditioned and passedthrough respective band pass filters (e.g., filters 284, 384, 484, 584,684, 784). These filters may be tuned for different ranges of frequencyspectrum. The bandwidth of these band pass filters may be determined byanalyzing the fault waveforms. The output of the HF band pass filtersmay be rectified and integrated to create envelopes that may be comparedwith set thresholds. The output may be stabilized by a monostable multivibrator and then transferred to the input port of the GFCU 120A. Asignal transition on this input port may indicate that the HF envelopehas crossed the threshold and further processing may be initiated.

In embodiments, one or more of the filters 584, 684, 784 may, forexample and without limitation, be configured as a Sallen-Key bandpassfilter.

With embodiments, such as generally illustrated in FIGS. 8, 10, 18 and20, an electrical system 100, may include an HF current sensor 238, 600(e.g., an HF current transformer). An example of an HF current sensor238, 600 is generally illustrated in FIG. 21. As generally illustratedin FIG. 22, an HF current sensor 238, 600 may be configured for sensingcurrents with frequencies of about 20 kHz up to 10 MHz, for example andwithout limitation. An HF current sensor 238, 600 may include two parts,such as a current transformer and a precisely tuned and matchedamplifier circuit. Ground current noise may be relatively low at highfrequencies, the HF current sensor (HF CS) may include a bigger gap core(e.g., model 58257A2). Such a sensor 238, 600 may include a variablegain and may not saturate at high currents. The HF current sensor 238,600 may provide better performance than other sensors. Performance of anLF current sensor 236 may decline around 1 kHz and may declinesignificantly around 10 kHz.

With embodiments, electrical systems 100 may be configured to detectground faults and may use one or more components/hardware of existingarc fault circuit breakers, such as those described in commonly ownedpatents U.S. Pat. Nos. 9,612,267, 9,768,605, 9,797,940, 9,797,941, and8,218,274, the disclosures of which are hereby incorporated by referencein their entireties. In embodiments, electrical systems 100 may providereliable ground fault detection over a wide frequency range.

In embodiments, a method of operating an electrical system 100 mayinclude operating a power source 102 to provide an AC voltage to a load106 and/or a transformer rectifier unit, such an ATRU 148, 222, 224. Themethod may include detecting ground fault current via a first GFD unit110 and/or a second GFD unit 120. The first GFD unit 110 may beconnected to an output of the power source 102. The second GFD 120 unitmay be connected to an output of the ATRU 148, 222, 224. An ECU 104 maybe connected to the first GFD unit 110 and/or the second GFD unit 120.The ECU 104 may be configured to monitor the first GFD unit 110 and/orthe second GFD unit 120 over time. For example and without limitation,the ECU 104 may be configured to indicate a ground fault if the firstGFD unit 110 and/or the second GFD unit 120 detects ground current for aperiod of time. An amplitude threshold for the ground current may belower than other ground fault detection systems, which may permit theelectrical system 100 to detect higher frequency and lower amplitudeground fault currents that may damage components over time (even if suchground current is not an immediate risk). For example and withoutlimitation, a threshold of high frequency ground current may be about 1A or less, about 500 mA or less, or other values.

With embodiments, an electrical system 100 may include a first thresholdfor low frequency ground current (e.g., 1 kHz or less) and/or mayinclude a second threshold for high frequency ground current (e.g.,greater than 1 kHz). The second threshold may be lower than the firstthreshold. A first time period (e.g., how long the threshold value maybe sensed before detecting a fault) may be associated with the firstthreshold and a second time period may be associated with the secondthreshold. The second period may be longer than the first threshold. Thesecond period may, for example and without limitation, be at least onesecond, at least one minute, and/or at least one hour, among othergreater and lesser values. The first period may, for example and withoutlimitation, be less than one minute, less than one second, and/or lessthan half of one second, among other greater and lesser values.

Embodiments of electrical systems 100 may be configured for highfrequency ground fault detection for MEA Loads, such as PMSM (permanentmagnet synchronous motor) motor controllers and/or VFDs (variablefrequency drives), among others. Embodiments of electrical systems 100may be configured to limit and/or avoid component failure, such asbearing failures for motors and generators. Embodiments of electricalsystems 100 may enable detection of ground faults of transformerrectifier units, such as of multi-pulse auto-transformers. Embodimentsof electrical systems 100 may not require FFT-based complex higher endmicrocontroller processing, DSP (digital signal processing), and/or FPGA(field programmable gate array) processing. Embodiments of electricalsystems 100 may be utilized in connection with carbon compositeaircraft. Embodiments of electrical systems 100 may include one or morecomponents common with arc fault detectors. Embodiments of electricalsystems 100 may be configured to compensate for and/or avoid saturationby high amplitude AC or DC over current faults (e.g., after clearing aDC ground fault, an AC ground fault may still be detected). Embodimentsof electrical systems 100 may provide the option not to trip for highfrequency ground current and may be configured to avoid an aliasingeffect or nuisance tripping, which might otherwise be caused by highfrequency getting demodulated and detected as low frequency.

In embodiments, an ECU (e.g., ECU 104, GFCU 110A, GFCU 120A) may includean electronic controller and/or include an electronic processor, such asa programmable microprocessor and/or microcontroller. In embodiments, anECU may include, for example, an application specific integrated circuit(ASIC). An ECU may include a central processing unit (CPU), a memory(e.g., a non-transitory computer-readable storage medium), and/or aninput/output (I/O) interface. An ECU may be configured to performvarious functions, including those described in greater detail herein,with appropriate programming instructions and/or code embodied insoftware, hardware, and/or other medium. In embodiments, an ECU mayinclude a plurality of controllers. In embodiments, an ECU may beconnected to a display, such as a touchscreen display.

Various embodiments are described herein for various apparatuses,systems, and/or methods. Numerous specific details are set forth toprovide a thorough understanding of the overall structure, function,manufacture, and use of the embodiments as described in thespecification and illustrated in the accompanying drawings. It will beunderstood by those skilled in the art, however, that the embodimentsmay be practiced without such specific details. In other instances,well-known operations, components, and elements have not been describedin detail so as not to obscure the embodiments described in thespecification. Those of ordinary skill in the art will understand thatthe embodiments described and illustrated herein are non-limitingexamples, and thus it can be appreciated that the specific structuraland functional details disclosed herein may be representative and do notnecessarily limit the scope of the embodiments.

Reference throughout the specification to “various embodiments,” “withembodiments,” “in embodiments,” or “an embodiment,” or the like, meansthat a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment.Thus, appearances of the phrases “in various embodiments,” “withembodiments,” “in embodiments,” or “an embodiment,” or the like, inplaces throughout the specification are not necessarily all referring tothe same embodiment. Furthermore, the particular features, structures,or characteristics may be combined in any suitable manner in one or moreembodiments. Thus, the particular features, structures, orcharacteristics illustrated or described in connection with oneembodiment/example may be combined, in whole or in part, with thefeatures, structures, functions, and/or characteristics of one or moreother embodiments/examples without limitation given that suchcombination is not illogical or non-functional. Moreover, manymodifications may be made to adapt a particular situation or material tothe teachings of the present disclosure without departing from the scopethereof.

It should be understood that references to a single element are notnecessarily so limited and may include one or more of such element. Anydirectional references (e.g., plus, minus, upper, lower, upward,downward, left, right, leftward, rightward, top, bottom, above, below,vertical, horizontal, clockwise, and counterclockwise) are only used foridentification purposes to aid the reader's understanding of the presentdisclosure, and do not create limitations, particularly as to theposition, orientation, or use of embodiments.

Joinder references (e.g., attached, coupled, connected, and the like)are to be construed broadly and may include intermediate members betweena connection of elements and relative movement between elements. Assuch, joinder references do not necessarily imply that two elements aredirectly connected/coupled and in fixed relation to each other. The useof “e.g.” in the specification is to be construed broadly and is used toprovide non-limiting examples of embodiments of the disclosure, and thedisclosure is not limited to such examples. Uses of “and” and “or” areto be construed broadly (e.g., to be treated as “and/or”). For exampleand without limitation, uses of “and” do not necessarily require allelements or features listed, and uses of “or” are intended to beinclusive unless such a construction would be illogical.

While processes, systems, and methods may be described herein inconnection with one or more steps in a particular sequence, it should beunderstood that such methods may be practiced with the steps in adifferent order, with certain steps performed simultaneously, withadditional steps, and/or with certain described steps omitted.

It is intended that all matter contained in the above description orshown in the accompanying drawings shall be interpreted as illustrativeonly and not limiting. Changes in detail or structure may be madewithout departing from the present disclosure.

It should be understood that an electronic control unit (ECU), a system,and/or a processor as described herein may include a conventionalprocessing apparatus known in the art, which may be capable of executingpreprogrammed instructions stored in an associated memory, allperforming in accordance with the functionality described herein. To theextent that the methods described herein are embodied in software, theresulting software can be stored in an associated memory and can alsoconstitute means for performing such methods. Such a system or processormay further be of the type having ROM, RAM, RAM and ROM, and/or acombination of non-volatile and volatile memory so that any software maybe stored and yet allow storage and processing of dynamically produceddata and/or signals.

It should be further understood that an article of manufacture inaccordance with this disclosure may include a non-transitorycomputer-readable storage medium having a computer program encodedthereon for implementing logic and other functionality described herein.The computer program may include code to perform one or more of themethods disclosed herein. Such embodiments may be configured to executevia one or more processors, such as multiple processors that areintegrated into a single system or are distributed over and connectedtogether through a communications network, and the communicationsnetwork may be wired and/or wireless. Code for implementing one or moreof the features described in connection with one or more embodimentsmay, when executed by a processor, cause a plurality of transistors tochange from a first state to a second state. A specific pattern ofchange (e.g., which transistors change state and which transistors donot), may be dictated, at least partially, by the logic and/or code.

What is claimed is:
 1. A method of monitoring an electrical system, themethod comprising: providing a ground fault detection unit; operating atransformer rectifier unit to provide DC power to a load; sensing, via acurrent sensor, a ground current at or about an output of thetransformer rectifier unit; and monitoring a sensor output from thecurrent sensor via the ground fault detection unit; wherein the groundfault detection unit is configured to detect ground faults atfrequencies of at least 30 kHz.
 2. The method of claim 1, wherein theground fault detection unit is configured to detect ground faults atfrequencies of at least 100 kHz.
 3. The method of claim 1, includingsensing, via a second current sensor, the ground current; wherein thecurrent sensor is configured as a high-frequency current sensor and thesecond current sensor is a low-frequency current sensor.
 4. The methodof claim 3, wherein current sensor is not a Hall Effect sensor; and thesecond current sensor is a Hall Effect sensor.
 5. The method of claim 1,wherein monitoring the sensor output includes monitoring the sensoroutput over a period of time; and the period of time is at least onehour.
 6. The method of claim 1, including detecting a ground fault ifthe ground current exceeds a first threshold or a second threshold. 7.The method of claim 6, wherein the first threshold is a low frequencycurrent threshold and the second threshold is a high frequency currentthreshold.
 8. The method of claim 7, wherein the second threshold islower than the first threshold.
 9. The method of claim 6, whereindetecting the ground fault includes detecting the ground fault if theground current exceeds the first threshold for a first period of time orif the ground current exceeds the second threshold for a second periodof time.
 10. The method of claim 9, wherein the second period of time islonger than the first period of time.
 11. The method of claim 6, whereinthe ground fault corresponds to ground current with a frequency of atleast 25 kHz; and detecting the ground fault includes detecting theground fault without a Fourier transform.
 12. An electrical system,comprising: a ground fault detection unit, including: a first groundfault detection circuit including a first portion and a second portion,the first portion and the second portion connected to a first currentsensor; and a second ground fault detection circuit including a firstportion and a second portion, the first portion and the second portionconnected to a second current sensor; wherein the first current sensorand the second current sensor are configured to sense current at orabout an output of a DC power supply.
 13. The electrical system of claim12, wherein the first portion of the first ground fault detectioncircuit includes a low pass filter having a cutoff frequency; the secondportion of the first ground fault detection circuit includes a firstbandpass filter with a first passband; the first portion of the secondground fault detection circuit include a second bandpass filter with asecond passband; and the second portion of the second ground faultdetection circuit includes a third bandpass filter with a thirdpassband.
 14. The electrical system of claim 13, wherein the thirdpassband includes higher frequencies than the second passband; thesecond passband includes higher frequencies than the first passband; andthe first passband includes frequencies above the cutoff frequency. 15.The electrical system of claim 13, wherein the DC power supply is atransformer rectifier unit; the first passband corresponds to the DCpower supply; the second passband corresponds to switching frequencies;and the third passband corresponds to harmonics of the switchingfrequencies.
 16. The electrical system of claim 14, wherein a maximumfrequency of the third passband is at least about 100 kHz and a maximumfrequency of the second passband is at least about 20 kHz.
 17. Theelectrical system of claim 16, wherein a maximum frequency of the secondpassband is at least about 4 kHz; and the cutoff frequency is about 10Hz or less.
 18. The electrical system of claim 12, wherein the firstportion of the second ground fault detection circuit includes ademodulator configured to reduce a frequency of an output of the secondcurrent sensor.
 19. The electrical system of claim 12, wherein the firstportion of the first ground fault detection circuit includes amonostable multivibrator.
 20. The electrical system of claim 12,including a second ground fault detection unit including a third groundfault detection circuit and a fourth ground fault detection circuit; thesecond ground fault detection unit is connected to an AC power supply;and the DC power supply is connected to the AC power supply andconfigured to convert AC power from the AC power supply to DC power fora variable frequency drive connected to an electric motor.